"The Queen has a busy schedule coming up including the Cop26 climate summit and of course next year the celebrations for her Platinum Jubilee," said a courtier.
"She wants to be in the best possible condition to enjoy those events next summer and doctors recently told her that cutting down on drink would be helpful. She made the personal decision to give up alcohol totally, but she has never been a heavy drinker."
Over the years, the Queen has been said to favour a gin and Dubonnet at lunchtime and a gin and vermouth cocktail before dinner.
For decades, Prince Philip – who preferred a beer – would mix her drink, knowing exactly how she liked it. "Perhaps losing her husband earlier this year took away some of the pleasure of a pre-dinner drink," said a source. "It was very much associated with the ritual of being with the Duke."
The Queen also enjoyed glass of rosé or German hock with dinner, but was never a big fan of Champagne. When she toasted visiting world leaders and other VIPs at banquets, she would be seen raising the glass to her lips but sipping only a small amount.
During one economy drive, she substituted expensive Champagne used for banquets with Tesco's own brand, telling an aide: "Who can tell the difference when it is served wrapped in white cloth?" At official receptions, she favoured a clear drink which, in photographs, could equally look like a mixed spirit or water.
The Queen's drinking tastes have long been a source of interest to the public.
With tales about her favourite drinks gathering momentum thanks to online news stories over the years, her former chef Darren McGrady moved to scotch rumours that the monarch was anything but a sensible drinker, saying: "She'd be pickled if she drank that much."
Earlier this week, the Queen was photographed using a walking stick for the first time in public since recovering from a knee operation in 2004. Courtiers said the stick, used during a visit to Westminster Abbey, was for her comfort alongside other small accommodations for her age.
The Queen is understood to be in excellent health for her age and has previously made only minor concessions to the practicalities of working in her 90s.
In 2016, she used a lift to enter Parliament for the State Opening, avoiding the 26 steps of the Royal Staircase at the Sovereign's Entrance. She has not worn the heavy Imperial State Crown since 2016, instead having it placed on a red and gold velvet cushion during the proceedings.
In the coming weeks, the monarch will be keeping up a remarkably busy programme. On Tuesday, she will host a Windsor Castle reception to mark the Global Investment Summit, with guests including the Prince of Wales and the Duke of Cambridge, Boris Johnson and business and investment leaders. Next month, she will attend the Cop26 summit in Glasgow.
